If this is your first visit, be sure to
check out the FAQ by clicking the
link above. You may have to register
before you can post: click the register link above to proceed. To start viewing messages,
select the forum that you want to visit from the selection below.

Help with a new mold not casting.

I have a new mold that I have tried to cast with but am getting poor results on one cavity.
This is the 3rd attempt at using this mold. It's a 4 cavity Accurate mold 35-115Z (9mm 115gn TC). I have cleaned the mold a couple of times.
I get about a 80-90% reject rate on cavity 3, and 30-40% on cavity 2. The base does not fill out.
Lead is 92-6-2. Temp is 740F (PID controlled), mold is 400F. I have tried between 390-420 for the mold temp, still the same issue.
Lee 4-20 bottom pour.
I have tried with fast and slow flow. Start at the back and cast to the front, start front and work to the back. Tight and loose sprue plate.
Just can't get good fill out of the base on that cavity. 1 and 4 are perfect.
I know these molds don't come with vent lines between the top and sprue plate, could this cause the issue?
Any idea would be appreciated.

Turn up the pouring rate so you drop the same amount of lead at a shorter time. If I pour too slow I get similar rounded bases and bad fillout. With your alloy you should not have this problem. Both melt and mould are hot enough

Are those pin hole cavities we see in the bullet bases? Sometimes it is hard to see the sprue hole when using the Lee 4-20 and if you pour off the side, the alloy might block the flow of air leaving the mold. Are you trying to fill all cavities in one movement, or do you start and stop at each sprue hole. You will need to tilt the top of the mold to avoid alloy flowing into the adjacent cavity. Try to create as large a sprue puddle as will stay on the sprue plate without running off the edge (only to avoid a mess, it will not cause problems with fill out) to continue to feed the cavity. I agree you might be filling the mold too slowly. I like a free flowing full stream to fill a mold of any size. More important with weights over 250 grains. If you had alloy spewing all over, I would have suggested you let the alloy level drop to about 2/3rds of the pot and not a full pot. Perhaps you are not working with a full pot with this smaller bullet and the flow is adversely affected? Less than full could affect the PID readings as well as the alloy flow.

I can think of two things I would try if this were my mould. First, prep the block tops and under side of the sprue plate with synthetic two cycle oil (heat, apply,cool and wipe) Application on block tops works better when there a boolits in the cavities. Second, some aluminium moulds are enhanced with a touch smoke (wooden stick match) - not much, just a tad. The smoke can always be cleaned off if need be.

One other thing, I would also break the top mating surface edge of the blocks with a stone to create a vent line - again, not much, just break the sharp edge.

Back to the 2-cycle oil. Elvis ammo has a video on youtube where he keeps a rag impregnated with oil and occasionally does a light wipe while casting. This techique works fairly well with some moulds.

Somewhere on here I read a post about putting a slight bevel on the top edge of a mould between the cavities. I use a stone to just ease each side with a 45*angle or so, to allow the air to escape, kinda like dulling a sharp edge. It does not take very much so go easy.

Breaking the sharp edge of the blocks creates one last vent line under the sprue plate. A very fine stone, fine jewelers file, or 600 grit sand paper glued to a piece of flat stock will work for this. Go slow you just need to break the edge at a 45* angle enough to see the fine line. To see this better blacken the top and face surfaces with a magic marker.

Sometimes a faster fill helps as does pouring a bigger sprue on top. These help keep the base hot and molten longer allowing for better venting. The bigger sprue also heats more of the sprue plate and adds some pressure to push gasses out.

The last to try is pressure pouring. Literally put the spout in the sprue hole open and give a 4-5 count lower handle and mould at same time to form sprue. This forces molten lead in under the pressure of the pots weight. If this works you may not want to cast at under 1/2 full to maintain pressures consistency.

Some moulds take longer to break in and develop the patina that aids in fill out and release. Some times a light smokeing helps but go easy as it can affect bullets dia. You want a dry smoke. A wood match, butane lighter. It doesn't take much.

Dismantle the mold and soak it in paint thinner for a day or three. Brush the mold thoroughly with a tooth bush. Be sure you get all the nooks and crannies. Now rinse again for a day or so in the paint thinner. Repeat as needed.

Blow it off and wash it with soap and hot water, Rinse thoroughly, then soak in water and swish around. You just want to be sure all residue form soap is removed. You can go back in CLEAN paint thinner if not sure its clean. Now blow it dry and set in the sun or oven on lowest setting for fifteen or so to be sure dry.

Start the melt and warm the mold as normal. (Assuming experience with this) Now cast as the mold comes up to temp it will cast as it should unless the problem is your methods. You now know its not the mold.

I had a couple that gave me problems recently as they where stored in oil and it permeated the steel so much that it did not cast well at all. This cured the problems.

As mentioned before
make sure the sprue plate and tom of mold are completely dry, any excess lube can prevent venting, excess lube can prevent fill out.
make sure sprue plate is not to tight and moves freely, it doesn't need to "drag on the mold" to work right and the mold will last longer if it doesn't
you can try smoking the sprue plate lightly then wiping it off completely,
It does look like you have a really tight fit along the top edge of the mold around that cavity. you can use a fine stone/diamond hone to lightly break the top edges of the mold to match an existing vent line (don't get carried away, you can't put the material back. If you do mess up you can have a couple thou machined off the top of the mold to fix over breaking.
you could try adding another .5 oz of tin

For perfectly filled out bullet with no wrinkles - give this a try at your next session:
* Heat a clean mold, the mold pins lubed with paraffin and the melt temperature to a temperature (usually 710-730 degrees) so after a 5 second pour of the melt, the sprue puddle frosts in 5 - 8 seconds. Then cut the sprues. The bullets will be completely filled out - the bases will be flat & sharp and with a consistent casting rhythm, the Bell Curve weight of the bullets will be less than 1 grain variance

I have a new mold that I have tried to cast with but am getting poor results on one cavity.
This is the 3rd attempt at using this mold. It's a 4 cavity Accurate mold 35-115Z (9mm 115gn TC). I have cleaned the mold a couple of times.
I get about a 80-90% reject rate on cavity 3, and 30-40% on cavity 2. The base does not fill out.
Lead is 92-6-2. Temp is 740F (PID controlled), mold is 400F. I have tried between 390-420 for the mold temp, still the same issue.
Lee 4-20 bottom pour.
I have tried with fast and slow flow. Start at the back and cast to the front, start front and work to the back. Tight and loose sprue plate.
Just can't get good fill out of the base on that cavity. 1 and 4 are perfect.
I know these molds don't come with vent lines between the top and sprue plate, could this cause the issue?
Any idea would be appreciated.

Thanks

I have no suggestions and it might totally be a coincidence but I recently got a Accurate four banger mold that does that exact same thing in that exact same hole. Mine is fairly random and I ladle pour so I just chalked it up to my technique being wonky. Weird coincidence though!

You could try this also. Hold the mold closer to the spout, and pour a very generous sprue puddle on top of the plate even if it spills over. Just make sure to have a pan or something to catch the overflow. I use an ingot mold for this. Your temps are a tad high for my liking, 725* is normally the sweet spot for me. You could also angle the mold very slightly so the lead will "swirl" a little as it enters the cavities.

So I put a really small chamfer along the top edge each mold half. You can't see it by eye but can feel the non-sharp edge.
Now the results. I went from 80% to 3 rejects out of 100+ pours. And all of those 3 I know I did a sloppy pour.
So I think the mold was made too well with a tight seal at the top and it was building pressure in that cavity.

I can think of two things I would try if this were my mould. First, prep the block tops and under side of the sprue plate with synthetic two cycle oil (heat, apply,cool and wipe) Application on block tops works better when there a boolits in the cavities. Second, some aluminium moulds are enhanced with a touch smoke (wooden stick match) - not much, just a tad. The smoke can always be cleaned off if need be.

One other thing, I would also break the top mating surface edge of the blocks with a stone to create a vent line - again, not much, just break the sharp edge.

Back to the 2-cycle oil. Elvis ammo has a video on youtube where he keeps a rag impregnated with oil and occasionally does a light wipe while casting. This techique works fairly well with some moulds.

I just got a new Lee 2 cavity mold for .375 round ball. I lit a painting stir stick to smoke it, and I think I went loco. It's smoked... pretty black! Should I clean it, then lightly smoke it, or will the balls drop okay after a few casts?